Learn Polish: Szanowny panie profesorze, proszę wejść. - Respected professor, please come in.

Because we are addressing the man directly, which means we need the Vocative case (Wołacz). For many masculine nouns, the Vocative is formed by adding an -e or -ie to the end of the word.

Why does profesor change to profesorze?

This is also the Vocative case in action! When a masculine noun ends in -r, adding the Vocative -e ending causes a spelling and sound change where the r becomes rz. So profesor becomes profesorze, just like doktor becomes doktorze.

If this is the Vocative case, why didn't the adjective Szanowny change its ending?

Adjectives give you a break here! In Polish, adjectives do not have a special, separate ending for the Vocative case. They simply use their regular Nominative (dictionary) form. That is why Szanowny stays exactly the same while the nouns it describes change.

How does the phrase proszę wejść translate to "please come in"?

The word proszę literally means "I ask" or "I request." To politely invite or tell someone to do something in Polish, you simply pair proszę with the infinitive (dictionary form) of the action verb. Here, wejść is the infinitive meaning "to enter" or "to come in."